1. Field of the Invention
This invention relates to files, and particularly, to files including a front cover portion and a back cover portion adjacently provided on both sides of a spine portion and further including clear pockets fastened between the front cover portion and the back cover portion, such as clear books and card albums.
2. Description of the Related Art
Conventionally, a file including clear pockets includes pockets that are made of clear films. The file including clear pockets is produced in an open state in which pockets are welded and fixed to the cover and file binding pockets are produced by melting the central portion of a stack of several pockets and welding the stack of pockets to the back portion of the cover.
In the file, the efficiency of page spread decreases when approaching both ends of the file due to the structure of the welded stack of pockets. Japanese Patent Application No. 5-32279, Japanese Utility Model Application No. 7-11434, and Japanese Patent Application No. 5-205490 disclose a file having an improved uniform spread at its center or at both ends by respectively welding each of a plurality of pockets to a cover.
Conventional files including pockets increasingly form a curve from a flat state as spread approaches the center by the thickness of the documents therein, even in a file in which each of the pockets is respectively welded to the cover, and as a result, efficiency of spread decreases.